Flash control electrode



Oct. 2, 1951 E. s. AUTlE EI'AL 2,569,968

FLASH CONTROL ELECTRODE Filgd Jan. 5, 1948 2 Sheets-Sheet 1 Oct. 2, 1951Filed Jan. 5, 1948 E I' firm/r015 E. G. AUTIE ET AL 2,569,968

FLASH CONTROL ELECTRODE 2 Sheets-,Sheet 2 Patented Oct. 2, 1951 FLASHCONTROL ELECTRODE Edward George Autie and Frederick William J ohnes,London, England, assignors to Applied High Frequency Limited, London,England, a

UNITED STATES PATENT OFFICE British company Application January 5, 1948,Serial No. 496 In Great Britain January 7, 1947 7 Claims.

the work.

a spot electrode.

been completed.

shall be prevented or minimised.

con i uou r v r pp h s rips, bars, 5 a recess to accommodate displacedplastic (or rods, flanges and the like in two or more layers, flash) andin this specification the separate elements In a preferred method, thespot electrode is will be referred toas pieces while the asaxiallymovable in relation to the surrounding sembly undergoing welding will bereferred to as pressure member and is resiliently controlled so Theexpression spot welding imthat softened plastic displaced during weldingplies that a particular weld or union is localised does not escape pastthe pressure member but within a restricted area of the work which areais accommodated within the area of the yieldmay be circular, elliptical,rectangular or of other ing spot electrode. suitable contour. As isknown (say in the case of The electrically-conducting spot electrode mayoverlapping sheets or strips) the weldingis efcomprise two concentricportions, viz. an outer fected between two metal electrodes each ofunyielding sleeve immediately within the pressure which is in contactwith one side of the work. member and a central resiliently-controlledOne of these electrodes may be a plate of a suryielding electrode, thearrangement being such face greater than the area of the weld or unionthat softened plastic displaced during welding is produced at onewelding operation. The other accommodated within the area of the centralelectrode (or each electrode) may have a conyielding electrode. tactface of substantially the same area and This invention also relates toapparatus for contour as the weld or union produced, and such spotwelding dielectric plastics by the use of higha localised electrode ishereinafter referred to as frequency electric heating which apparatuscomprises two electrodes to engage opposite faces Typical examples ofdielectric thermoplastic of the work, one at least of said electrodesbematerials which can be welded are methyl mething a spot electrodewhich is surrounded by a reacrylate polymer, polyvinyl chloride orpolyvinyl fractory insulating pressure member having reacetate. Typicalexamples of dielectric thermosilient means for pressing it into contactwith the setting materials which can be Welded are the work to preventextrusion of displaced material condensation products ofphenol-formaldehyde radially or laterally outwards from the spot elecorureaformaldehyde before condensation has trode.

In a preferred form of the apparatus the It is a common experience thatwhen any maspot electrode comprises two concentric parts, terial in asoftened or plastic state is subjected viz. an unyielding cylindricalsleeve immedito local pressure, material under pressure is disatelywithin the pressure member and a central, placed or extruded. Thus iftwo overlapping resiliently-controlled yielding electrode axially stripsof thermoplastic material be softened by movable in relation to thesleeve so that during heat and subject to welding pressure, extruded awelding operation, the contact face of the sleeve material or flashescapes laterally or radially applies steady pressure to the work anddisplaced outwards from the area of the weld. One subject plastic cannotescape radially outwards but is of this invention is to provide a methodand apaccommodated within the area of the contact paratus for thewelding of dielectric plastics by face of the central yieldingelectrode. the use of high-frequency electric heating and by Theinvention will be more clearly understood the use of pressure in whichsuch escape laterally from the following description of an example, orradially outwards from the area of the weld reference being made to thedrawings in which:

Fig. 1 is a sectional elevation of a spot weld- This invention relatesto a method of welding ing electrode, pieces of dielectric plastics bythe use of high- Figure 2 is an elevation of a welding press, frequencyelectric heating in which a spot elec- Figure 3 is a sectional elevationon an entrode is surrounded by a pressure member of relarged scaleshowing the welding of two pieces fractory insulating material'pressedinto contact of thermoplastic. with one face of the work so that whensoften- Figure 4 is a plan of one alternative form of ing and weldingtake place, escape or extrusion Welded strips.

Referring to Figure 1, a pressure member iii of the die ectric p astmate a cannot take p ace radially or laterally outwards and anydisplaced material is retained under the contact face of the spotelectrode.

The spot electrode may have on its contact face made of refractoryinsulating material is enclosed in an insulating sleeve l6 and isaxially movable in said sleeve under the resilient control of a springll lying between the upper surface of the pressure member 15 and anadjusting collar l8 which is in screw engagement with a sleeve l9 whichhas a head 29 secured to the outer insulating sleeve lb. The sleeve I9is of metal, say copper, and has a contact face 2! which forms anoperative part of the spot electrode. The sleeve 19 has at its lower enda cylindrical recess 22 and at its upper end another cylindrical recess23. Within the sleeve 19 is a central rod 24 carrying at its lower endthe inner yielding electrode 25 which in this case has a fiat contactface 26. In the recess 23 is a spiral spring 2? which applies yieldingpressure to the inner electrode 25 and the compression in the spring 21can be regulated by a slotted plug 28 which can screw within the top ofthe metal sleeve l9.

To regulate the movement of the pressure member 15 it is provided at itsperiphery with short vertical slots 29 engaging the inner end of screws30 passing through the outer insulating sleeve [6.

Figure 2 indicates the general arrangement of the welding press. Thelower electrode 3| is a plate held in a fixed support 32. The upper partof the metal sleeve I9 is inserted into a cylindrical electrode holder33 and is secured therein by a screw 34. The electrode holder 33 formspart of the movable member 35 of the press.

Referring'to Figure 3, a lower piece of thermoplastic 35 lies in contactwith the plate 31 and an upper piece of thermoplastic 3'! lies incontact with the lower piece 38 and is subjected to pressure not only bythe pressure member but also by the contact face 21 of the conductingsleeve l9 and the contact face 25 of the inner electrode 25. Thehigh-frequency alternating electric field is set up betweenthe'electrode plate 3! and the composite spot electrode I9, 25. Thematerial of the work directly between the electrodes softens and thecontact face 2| of the unyielding sleeve [9 exerts a maximum pressure onthe work. The spring I! keeps the contact face of the pressure member l5in firm contact with the face of the work and prevents escape ofdisplaced plastic radially outwards. The displaced plastic acts on thecontact face 25 of the yielding electrode 25 as indicated in Figure 3.

In the arrangement shown the pieces of thermoplastic 36 and 31 are inclose contact but it will be understood that in certain circumstancesthey may be separated (except at the weld) by an interlayer or by an airspace.

The pressure exerted by the springs I! and 21 is adjusted at will.

It will be understood that when under the action of the heat andpressure the plastic softens, a single mass of plastic is formed betweenthe electrodes by the complete union of the two (or more) layers ofplastic as indicated in Figure 3.

If desired the travel of the upper electrode as a whole may be arrestedwhen a predetermined separation from the lower electrode is reached.

Normally the contact face 21 of the sleeve l9 produces an annulardepression in the upper surface of the plastic and the softened andextruded plastic under the contact face 25 of the yielding electrode 25produces a substantially circular flat-topped protuberance or stud.However the contact face of the yielding electrode 25 (or electrodes ifmore than one be used) can take 4 various forms to produce any desiredconfiguration on the weld.

Thus as indicated in Figure 4 although the two layers 36 and 31 areunited between the electrodes, the annular depression 38 is formed byannular contact face 2| while two spots 39 may be formed by the contactface 25.

We claim:

1. A spot welding electrode, for use in the spot welding of dielectricplastic material by high frequency electric heating, comprising aconducting sleeve providing an annular end face at one end forengagement with the work to be welded, a conducting plunger slidablewithin the sleeve and in electrical contact therewith, which plunger hasits end face corresponding to the said end face of the sleeve arrangedfor engagement with the work, resilient means operating to urge theplunger to slide within the sleeve in the direction towards said annularface and outwardly of the sleeve, said resilient means being arranged sothat when the end face of the plunger is substantially flush with theend face of the sleeve, said resilient means are lightly loaded andpermit inward movement of the plunger under pressure applied to the endthereof during welding thereby to form a recess in the end of theelectrode for reception of softened plastic material displaced duringwelding which recess is bounded by the sleeve and said end face of theplunger, and a heat-resisting insulating pressure member surroundingsaid sleeve and providing around the end of the sleeve a face forengagement with the work.

2. An electrode as claimed in claim 1 and including stop means arrangedto prevent outward movement of the plunger beyond a position in whichthe said end face thereof protrudes a short distance beyond the end ofthe sleeve.

3. A spot welding electrode, for use in the spot welding of dielectricplastic material by high frequency electric heating, comprising aconducting sleeve providing an annular end face at one end forengagement with the work to be welded, a conducting plunger slidablewithin the sleeve and in electrical contact therewith, which plunger hasits end face corresponding to the said end face of the sleeve arrangedfor engagement with the work, first resilient means operating to urgethe plunger to slide within the sleeve in the direction towards saidannular face and outwardly of the sleeve, said first resilient meansbeing arranged so that when the end face of the plunger is substantiallyflush with the end face of the sleeve, said first resilient means arelightly loaded and permit inward movement of the plunger under pressureapplied to the end thereof during welding thereby to form a recess inthe end of the electrode for reception of softened plastic materialdisplaced during welding which recess is bounded by the sleeve and saidend face of the plunger, a heat-resisting insulating pressure membersurrounding and slidable along said sleeve and providing around the endof the sleeve a face for engagement with the work, and second resilientmeans urging said pressure member along the sleeve to make pressurecontact with the work.

4. An electrode as claimed in claim 3, in which the plunger is arrangedcentrally within the sleeve.

5. An electrode as claimed in claim 4, in which the said end face of theplunger is embossed with a design.

6. A spot welding electrode, for use in welding dielectric plasticmaterial by the use of high frequency electric heating, comprising atubular shell, a conducting sleeve extending within the shell lengthwisethereof, rigidly secured thereto and having one end projecting from oneend of the shell, which sleeve provides an annular face at itsprojecting end for engagement with the work to be welded, a conductingplunger slidably received within the sleeve and in electrical contacttherewith, which plunger has an end face for engagement with the work,first resilient means urging the plunger outwardly of the sleeve, in adirection towards the projecting end thereof, as far as a position inwhich the said face of the plunger lies adjacent the projecting end ofthe sleeve, stop means for preventing further movement of the plungerbeyond said position in said direction, a heat-resisting insulatingpressure member closely surrounding said sleeve within the shell andprojecting from said shell, at the same end as the sleeve projects, toprovide an annular face for engagement with the work at a positionaround and adjacent to said face of the sleeve, second resilient means,acting between the pressure member and an abutment rigidly secured tosaid shell, urging said pressure member outwardly of the shell to applypressure to the work, and stop means limiting the movement of thepressure member in a direction outwardly of the shell.

7. A spot electrode for use in welding dielectric plastic material bythe use of high frequency electric heating comprising a cylindricalelectrically-insulating shell, a refractory insulating pressure memberconcentric with said shell and axially-movable therewithin in-relationthereto 6 against the resilient restraint imposed by a helical springpositioned between the pressure member and an abutment on said shell, anelectrically-conducting sleeve rigidly secured to said shell, concentrictherewith, and passing through said pressure member with the extremityintended to contact the work approximately coplanar with the extremityof the pressure member intended to contact the work when in itsoutwardly extreme position, an electrically conducting cylinderconcentric with and surrounded by said sleeve and axially movablerelative thereto and a helical spring positioned between a secondabutment on said shell and said cylinder.

EDWARD GEORGE AUTIE. FREDERICK WILLIAM J OHNES.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,244,455 Gengenbach June 3, 19412,354,714 Strickland Aug. 1, 1944 2,401,991 Walton et a1. June 11, 19462,422,525 Brown et a1 June 17, 1947 2,423,902 Peterson July 15, 19472,425,123 Quayle et a1 Aug. 5, 1947 2,434,025 Wallace Jan. 6, 19482,445,747 Watter 1 July 20, 1948 2,472,820 Graham et a1 June 14, 1949FOREIGN PATENTS Number Country Date 591,738 Great Britain 1 Aug. 27,1947

